The present invention relates generally to energy storage devices, such as capacitors, and more particularly to high surface area electrodes for use in fabricating high energy density storage capacitors for low voltage applications.
Technology related to the invention is described in U.S. Pat. No. 5,151,848 to Finello, entitled "Supercapacitor," the entire teachings of which are incorporated here by reference. In Finello '848 a supercapacitor and process for making it are described wherein a pair of ruthenia coated titanium electrodes are placed about a membrane of solid polymer electrolyte, which assembly is placed into a high pressure shock apparatus for impregnation of the polymer into the porous electrodes.
In accordance with the teachings of the present invention, high surface area molybdenum nitride (Mo.sub.2 N and MoN) electrodes may be fabricated by a process of coating a metallic substrate with molybdenum oxide (MoO.sub.3) and subsequent topotactic conversion of the MoO.sub.3 to Mo.sub.2 N and MoN by reaction with anhydrous ammonia to form a high surface area Mo.sub.2 N and MoN adherent coating bonded to the substrate, or by an alternative process of depositing (as by chemical vapor deposition (CVD)) molybdenum pentachloride (MoCl.sub.5) and subsequent reaction with ammonia (NH.sub.3) to form an adherent Mo.sub.2 N and MoN coating on a metallic or nonmetallic substrate.
Electrodes fabricated according to the invention can be incorporated into an ultracapacitor structure exhibiting high energy density (greater than one farad/cm.sup.2 of electrode sheet) at cell voltages to the limit of the electrolyte. Double-sided coated electrodes of the invention may be incorporated into bipolar cell stacks or rolled single cells. High energy density ultracapacitors structured using electrodes of the invention find substantial utility in devices requiring compact, low voltage energy sources which can be powered up after long periods of idle storage, such as in electric vehicles, rechargeable appliances and electronics, industrial robotics, portable power supplies for welding, demolition, mining, etc, medical electronics, defibrillators and wing de-icing.
It is therefore a principal object of the invention to provide a high surface area electrode.
It is another object of the invention to provide a process for fabricating high surface area electrodes.
It is yet another object of the invention to provide high surface area Mo.sub.2 N and MoN electrodes for use in energy storage devices.
It is a further object of the invention to provide an improved high energy density capacitor.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.